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Announcements. Homework 21: due Tuesday, Nov. 30, 2004 Review session before final. Chapter 16: Waves-I. Reading assignment: Chapter 17 Homework : (due Friday, Nov. 11, 2004): Problems: Q3, Q12, 7, 8, 13, 31, 34, 35, 47 . Waves are closely related to oscillations

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Announcements

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  1. Announcements • Homework 21: due Tuesday, Nov. 30, 2004 • Review session before final

  2. Chapter 16: Waves-I Reading assignment: Chapter 17 Homework : (due Friday, Nov. 11, 2004): Problems: Q3, Q12, 7, 8, 13, 31, 34, 35, 47 • Waves are closely related to oscillations • We’ll mainly deal with sinusoidal waves. • - Water waves: Water molecules oscillate in a circle • - Sound waves: Air molecules oscillate back and forth • - Stadium waves: People move up and down • - Electromagnetic wave: (in Physics 114)

  3. Waves: • Propagation of a disturbance through a medium • “Wave flees the place of its creation, while water [particle] does not” • - Water waves: Water molecules oscillate up and down • - Sound waves: Air molecules oscillate back and forth • - Stadium waves: People move up and down All waves carry (propagate) energy

  4. Traveling waves Transverse waves: Transverse waves: The particles of the disturbed medium move perpendicular to the wave motion particle wave

  5. Traveling waves Longitudinal waves: The particles of the disturbed medium move parallel to the wave motion Longitudinal waves:

  6. Examples of waves: “Bump” traveling down a rope:___________________ Compression of a slinky:_____________________ Sound waves:____________________ La ola in a stadium (getting up/sitting down):_____________ Water wave: ____________________________

  7. Basic Variables of Wave Motion Terminology to describe waves • Crest: “Highest point” of a wave • Wavelength l: Distance from one crest to the next crest. • Wavelength l: Distance between two identical points on a wave. • Period T: Time between the arrival of two adjacent waves. • Frequency f: 1/T, number of crest that pass a given point per unit time

  8. Sinusoidal waves Brown curve: Snap shot at time t = 0 Blue curve: Snap shot at later time.

  9. Sinusoidal waves The function describing a traveling sinusoidal wave:

  10. Sinusoidal waves

  11. Black board example 17.1 Traveling sinusoidal wave A sinusoidal wave traveling in the positive x-direction has an amplitude of 15.0 cm, a wavelength of 40.0 cm, and a frequency of 8.00 Hz. • Find the wave number k, the period T, the angular frequency w and propagation speed v of the wave. • If the vertical displacement of the medium at t = 0 and x = 0 is also 15.0 cm, what is the phase constant F? • Write a general expression for the wave function.

  12. Speed of waves on a string Transverse wave: Speed of wave Where: T… tension in rope (don’t confuse with period T) m… mass per unit length of rope

  13. Black board example 17.2 Speed of pulse in cord • A uniform cord has a mass of 0.300 kg and a length of 6.00 m. The cord passes over a pulley and supports a 2.00 kg object as shown. • Find the speed of a pulse traveling along this cord. • Find the time it takes the pulse to travel from the wall to the pulley

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